Method for reforming amorphous carbon polymer film

ABSTRACT

A method for reforming an amorphous carbon film as part of a deposition process thereof, includes process of: (i) depositing an amorphous carbon film on a substrate in a reaction space until a thickness of the amorphous carbon film reaches a predetermined thickness, and then stopping the deposition process; and (ii) exposing the amorphous carbon film to an Ar and/or He plasma in an atmosphere substantially devoid of hydrogen, oxygen, and nitrogen.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 62/844,705 filed on May 7, 2019, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention generally relates to a method for reforming an amorphous carbon polymer film, particularly, with respect to thermal stability.

Description of the Related Art

In processes of fabricating integrated circuits such as those for shallow trench isolation, inter-metal dielectric layers, passivation layers, etc., it is often necessary to fill trenches (any recess typically having an aspect ratio of one or higher) with insulating material. However, with miniaturization of wiring pitch of large scale integration (LSI) devices, void-free filling of high aspect ratio spaces (e.g., AR≥3) becomes increasingly difficult due to limitations of existing deposition processes.

Further, in order to densify deposited films, repair damage from ion bombardment, and/or improve chemical/physical properties, annealing of a deposited film is often performed. In this disclosure, “annealing” refers to a process applied to a film having a film matrix already formed, during which a film/layer is treated to be changed to its stable form, e.g., to change a terminal group to a more stable group (e.g., removal of hydrogen-containing terminals), which is distinguished from “curing” which is a process applied to a layer to form a film matrix.

Although an amorphous carbon polymer film is useful in gap-fill technology and/or in patterning as, e.g., a hardmask, a conventional amorphous carbon polymer typically has a high thermal shrinkage. When significant shrinkage occurs, an amorphous carbon polymer film is likely to be detached from a contacting surface and/or to undergo a deterioration its properties.

In view of the conventional gap-fill technology and/or patterning technology, an embodiment of the present invention which, however, is not limited thereto provides a method of forming an amorphous carbon polymer film having high thermal stability.

Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion were known at the time the invention was made.

When an amorphous carbon polymer film is formed by using a plasma-assisted method, the resultant amorphous carbon polymer film is constituted by hydrogenated amorphous carbon polymer. In this disclosure, a hydrogenated amorphous carbon polymer may simply be referred to an amorphous carbon polymer, which may also be referred to as “aC:H” or simply “aC” as an abbreviation. Further, in this disclosure, SiC, SiCO, SiCN, SiCON, or the like is an abbreviation indicating a film type (indicated simply by primary constituent elements) in a non-stoichiometric manner unless described otherwise.

SUMMARY OF THE INVENTION

In some embodiments, a method for reforming an amorphous carbon polymer film as part of a deposition process thereof, comprises process of: (i) depositing an amorphous carbon polymer film on a substrate in a reaction space until a thickness of the amorphous carbon polymer film reaches a predetermined thickness, and then stopping the deposition process; and (ii) exposing the amorphous carbon polymer film to an Ar and/or He plasma in an atmosphere substantially devoid of hydrogen, oxygen, and nitrogen. Accordingly, thermal stability of the amorphous carbon polymer film can significantly be improved. The “atmosphere substantially devoid of hydrogen, oxygen, and nitrogen” refers to no gas containing hydrogen, oxygen, or nitrogen being fed to the reaction space wherein a residual gas and/or gas released from a film which may contain hydrogen, oxygen, and/or nitrogen may be present as impurities or immaterial components. In some embodiments, in process (ii), solely Ar and/or He gas in non-excited state are/is fed to the reaction space and excited by RF power applied to electrodes, e.g., capacitively-coupled flat electrodes, provided in the reaction space, or solely Ar and/or He gas in an excited state are/is fed to the reaction space.

In some embodiments, process (ii) is cyclically conducted after every 1 nm to 15 nm of film growth in process (i).

For purposes of summarizing aspects of the invention and the advantages achieved over the related art, certain objects and advantages of the invention are described in this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

Further aspects, features and advantages of this invention will become apparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described with reference to the drawings of preferred embodiments which are intended to illustrate and not to limit the invention. The drawings are greatly simplified for illustrative purposes and are not necessarily to scale.

FIG. 1A is a schematic representation of a PEALD (plasma-enhanced atomic layer deposition) apparatus for depositing a dielectric film usable in an embodiment of the present invention.

FIG. 1B illustrates a schematic representation of a precursor supply system using a flow-pass system (FPS) usable in an embodiment of the present invention.

FIG. 2 is a graph showing shrinkage of amorphous carbon polymer films without plasma treatment (“STD”), with Ar plasma treatment (“Ar”), and with He plasma treatment (“He”) after annealing under different conditions, wherein “Ar” and “He” represent embodiments of the present invention.

FIG. 3 shows Fourier Transform Infrared (FTIR) spectrums of amorphous carbon polymer films without plasma treatment (“STD”), with Ar plasma treatment (“Ar”), and with He plasma treatment (“He”), wherein “Ar” and “He” represent embodiments of the present invention.

FIG. 4 shows a STEM photograph of a cross-sectional view of trenches subjected to a gap-fill process with He plasma treatment according to an embodiment of the present invention, wherein arrows show slightly darker interfaces indicative of He plasma treatment.

FIG. 5 is a chart illustrating the sequence of processes of film formation according to an embodiment of the present invention, wherein a cell in gray represents an ON state whereas a cell in white represents an OFF state, and the width of each column does not represent duration of each process.

DETAILED DESCRIPTION OF EMBODIMENTS

In this disclosure, “gas” may include vaporized solid and/or liquid and may be constituted by a single gas or a mixture of gases, depending on the context. Likewise, an article “a” or “an” refers to a species or a genus including multiple species, depending on the context. In this disclosure, a process gas introduced to a reaction chamber through a showerhead may be comprised of, consist essentially of, or consist of a silicon-free hydrocarbon precursor and an additive gas. The additive gas may include a plasma-generating gas for exciting the precursor to form an amorphous carbon polymer when RF power is applied to the additive gas. The additive gas may be an inert gas which may be fed to a reaction chamber as a carrier gas and/or a dilution gas. The additive gas may contain no reactant gas for oxidizing or nitriding the precursor. Alternatively, the additive gas may contain a reactant gas for oxidizing or nitriding the precursor to the extent not interfering with plasma polymerization forming an amorphous carbon-based polymer. Further, in some embodiments, the additive gas contains only a plasma-generating gas (e.g., noble gas). The precursor and the additive gas can be introduced as a mixed gas or separately to a reaction space. The precursor can be introduced with a carrier gas such as a rare gas. A gas other than the process gas, i.e., a gas introduced without passing through the showerhead, may be used for, e.g., sealing the reaction space, which includes a seal gas such as a rare gas. In some embodiments, the term “precursor” refers generally to a compound that participates in the chemical reaction that produces another compound, and particularly to a compound that constitutes a film matrix or a main skeleton of a film, whereas the term “reactant” refers to a compound, other than precursors, that activates a precursor, modifies a precursor, or catalyzes a reaction of a precursor, wherein the reactant may provide an element (such as O, C, N) to a film matrix and become a part of the film matrix, when in an excited state. The term “plasma-generating gas” refers to a compound, other than precursors and reactants, that generates a plasma when being exposed to electromagnetic energy, wherein the plasma-generating gas may not provide an element (such as O, C, N) to a film matrix which becomes a part of the film matrix. The term “reforming gas” refers to a gas which reforms a film already deposited, when in an excited state, typically without further growing the film (without any precursor). In some embodiments, the “reforming gas” is a plasma-generating gas.

In some embodiments, “film” refers to a layer continuously extending in a direction perpendicular to a thickness direction substantially without pinholes to cover an entire target or concerned surface, or simply a layer covering a target or concerned surface. In some embodiments, “layer” refers to a structure having a certain thickness formed on a surface or a synonym of film or a non-film structure. A film or layer may be constituted by a discrete single film or layer having certain characteristics or multiple films or layers, and a boundary between adjacent films or layers may or may not be clear and may be established based on physical, chemical, and/or any other characteristics, formation processes or sequence, and/or functions or purposes of the adjacent films or layers. Further, in this disclosure, any two numbers of a variable can constitute a workable range of the variable as the workable range can be determined based on routine work, and any ranges indicated may include or exclude the endpoints. Additionally, any values of variables indicated (regardless of whether they are indicated with “about” or not) may refer to precise values or approximate values and include equivalents, and may refer to average, median, representative, majority, etc. in some embodiments. Further, in this disclosure, the terms “constituted by” and “having” refer independently to “typically or broadly comprising”, “comprising”, “consisting essentially of”, or “consisting of” in some embodiments. In this disclosure, any defined meanings do not necessarily exclude ordinary and customary meanings in some embodiments.

In this disclosure, “continuously” refers to without breaking a vacuum, without interruption as a timeline, without any material intervening step, without changing treatment conditions, immediately thereafter, as a next step, or without an intervening discrete physical or chemical structure between two structures other than the two structures in some embodiments.

In this disclosure, a “recess or step” refers to any structure having a top surface, a sidewall, and a bottom surface formed on a substrate, which may continuously be arranged in series in a height direction or may be a single recess or step, and which may constitute a trench, a via hole, or other recesses. In this disclosure, a recess between adjacent protruding structures and any other recess pattern is referred to as a “trench”. That is, a trench is any recess pattern including a hole/via and which has, in some embodiments, a width of about 20 nm to about 100 nm (typically about 30 nm to about 50 nm) (wherein when the trench has a length substantially the same as the width, it is referred to as a hole/via, and a diameter thereof is about 20 nm to about 100 nm), a depth of about 30 nm to about 100 nm (typically about 40 nm to about 60 nm), and an aspect ratio of about 2 to about 10 (typically about 2 to about 5). The proper dimensions of the trench may vary depending on the process conditions, film compositions, intended applications, etc.

In some embodiments, a method for reforming an amorphous carbon polymer film as part of a deposition process thereof, comprises two processes: (i) depositing an amorphous carbon polymer film on a substrate in a reaction space until a thickness of the amorphous carbon polymer film reaches a predetermined thickness, and then stopping the deposition process; and (ii) exposing the amorphous carbon polymer film to an Ar and/or He plasma in an atmosphere substantially devoid of hydrogen, oxygen, and nitrogen.

In some embodiments, the amorphous carbon polymer film is a flowable film, and in other embodiments, the amorphous carbon polymer film is a non-flowable film.

Deposition of flowable film is known in the art; however, conventional deposition of flowable film uses chemical vapor deposition (CVD) with constant application of RF power, since pulse plasma-assisted deposition such as PEALD is well known for depositing a conformal film which is a film having characteristics entirely opposite to those of flowable film. In some embodiments, flowable film is a silicon-free carbon-containing film constituted by an amorphous carbon polymer, and although any suitable one or more of hydrocarbon precursors can be candidates, in some embodiments, the precursor includes an unsaturated or cyclic hydrocarbon having a vapor pressure of 1,000 Pa or higher at 25° C. In some embodiments, the precursor is at least one selected from the group consisting of C2-C8 alkynes (C_(n)H_(2n-2)), C2-C8 alkenes (C_(n)H_(2n)), C2-C8 diene (C_(n)H_(n+2)), C3-C8 cycloalkenes, C3-C8 annulenes (C_(n)H_(n)), C3-C8 cycloalkanes, and substituted hydrocarbons of the foregoing. In some embodiments, the precursor is ethylene, acetylene, propene, butadiene, pentene, cyclopentene, benzene, styrene, toluene, cyclohexene, and/or cyclohexane.

In some embodiments, as the gap-fill technology for deposition of flowable film, the method disclosed in U.S. patent application Ser. No. 16/026,711 can be used, which provides complete gap-filling by plasma-assisted deposition using a hydrocarbon precursor substantially without formation of voids under conditions where a nitrogen, oxygen, or hydrogen plasma is not required, the disclosure of which is herein incorporated by reference in its entirety.

By changing deposition conditions or process parameters, a non-flowable film can be formed. For example, such parameters include, but are not limited to, partial pressure of precursor, deposition temperature, deposition pressure, etc. For example, by increasing the deposition temperature, decreasing the deposition pressure, and/or decreasing the precursor ratio (a ratio of precursor flow to carrier/dilution gas flow), the flowability of film becomes low. In some embodiments, process (i) (deposition process) is conducted by plasma-enhanced atomic layer deposition (PEALD) or other cyclic plasma-assisted deposition (e.g., cyclic PECVD). As a plasma, a capacitively coupled plasma, inductively coupled plasma, remote plasma, a plasma generated by RF power, a plasma generated by microwaves, etc. can be used.

In some embodiments, when the thickness of deposited film in process (i) (deposition process) reaches a monolayer thickness or more but 15 nm or less, preferably 10 nm or less, more preferably 5 nm or less, the deposition process is stopped, followed by process (ii) (reformation process). As the film thickness increases prior to process (ii) (after the previous process (ii) if any), the overall reforming effect decreases. If the film thickness is larger than a maximum depth which the reforming effect by the treatment can be obtained, film quality/properties in a depth/thickness direction become inhomogeneous. If the film thickness is sufficiently small for receiving the reforming effect by the treatment, film quality/properties in the depth/thickness direction become homogeneous, thereby uniformly suppressing shrinkage of the film when subjected to subsequent annealing or other high thermal budget processes at, e.g., 200° C. to 400° C.

In some embodiments, processes (i) and (ii) are repeated multiple times until a thickness of the amorphous silicon film reaches a desired final thickness.

In some embodiments, the atmosphere in process (ii) is in the reaction space used in process (i), wherein process (i) and process (ii) can be performed continuously. Alternatively, in other embodiments, the atmosphere in process (ii) is in another reaction space different from the reaction space used in process (i).

In some embodiments, process (ii) comprises: feeding Ar and/or He to the atmosphere without feeding hydrogen, oxygen, and nitrogen; and applying electromagnetic energy to the atmosphere in a manner generating Ar and/or He plasma. As a plasma, although a capacitively coupled plasma may typically be used, inductively coupled plasma, remote plasma, a plasma generated by RF power, a plasma generated by microwaves, etc. can also be used. In some embodiments, a He plasma is most effective. The Ar and/or He plasma can reduce thermally unstable hydrogen-related fractions such as methyl and/or methylene fractions from the amorphous carbon polymer film (e.g., by further promoting polymerization, rather than by separating the fractions), thereby increasing thermal stability of the film.

In some embodiments, RF power is in a range of 0.06 W/cm² to 0.96 W/cm² per unit area of the substrate, and a duration of process (ii) is in a range of 2 seconds to 300 seconds, so that the plasma treatment can effectively reform the amorphous carbon polymer film.

In some embodiments, the plasma treatment (the reformation process) can be conducted under conditions described below.

As a reforming gas for the plasma treatment, Ar and/or He gas is used as a primary gas. Substantially no precursor nor reactant is fed to the reaction space while conducting the reformation process for most effective treatment; however, the atmosphere of the reaction space may be contaminated by impurities or unintended components such as residual gas left in the atmosphere even after purging and/or gas released from the film as a result of the plasma treatment. Gas other than Ar or He may be present in the atmosphere of the reaction space as long as the atmosphere is substantially devoid of hydrogen, oxygen, and nitrogen. These elements typically interfere with reforming reaction by the Ar and/or He plasma treatment. For example, if H₂ is added to the reaction space during the reformation process, the amorphous carbon polymer film may be ashed. By using substantially solely Ar and/or He, the thermal stability of the amorphous carbon polymer film can dramatically be improved. In some embodiments, a gas volume ratio of Ar/He in the reaction space is in a range of 1/0 to 0/1 during the reformation process.

As for the reformation temperature, when the treatment is carried out in situ typically in a cyclic manner, preferably, the temperature is compatible with the flowable deposition (e.g., <125° C.). When the treatment is applied ex situ in a different chamber or on none-flowable film, there is no restriction imposed on the temperature (e.g., <800° C.).

As for RF power for the reformation process, in some embodiments, an RF power of 50-800 W, preferably 200-600 W, is applied to the electrodes as measured for a 300-mm wafer (RF power can be calculated for a different size wafer using RF power (W/cm²) calculated per unit area of a 300-mm wafer).

As for the duration of the reformation process, in some embodiments, the plasma treatment (a period of applying RF power) is continued for 2-300 seconds, preferably 10-30 seconds.

In some embodiments, the substrate has a patterned recess or step on its surface on which the amorphous carbon polymer film is deposited, although the reformation process is also applicable to the amorphous carbon polymer film deposited on a planar surface as a blanket carbon polymer film.

The embodiments will be explained with respect to the drawings by way of example and without any limitation.

FIG. 5 is a chart illustrating the sequence of processes of film formation according to an embodiment of the present invention, wherein a cell in gray represents an ON state whereas a cell in white represents an OFF state, and the width of each column does not represent duration of each process. By this reforming technique, thermal stability of an amorphous carbon polymer film can significantly be improved, and also dry etch rate of the film can significantly be lowered.

This process sequence comprises a deposition process (“Feed”→“Purge”→“RF Pulse-1” (plasma polymerization)→“Purge”), and a plasma treatment process (“Stabilize”→“RF Pulse-2” (plasma reformation)→“Purge”). The plasma polymerization process comprises depositing an amorphous carbon polymer film on surfaces of a step on a substrate by PEALD using a Si- and metal-free, C-containing precursor and a plasma-generating gas which generates a plasma by applying RF power (RF) between two electrodes between which the substrate is placed in parallel to the two electrodes, wherein RF power is applied in each monolayer deposition cycle of PEALD, wherein the plasma-generating gas and the carrier gas flow continuously and function also as a purging gas during “Purge” after “Feed” and during “Purge” after “RF Pulse-1”.

The deposition process is a PEALD process, one cycle of which for forming a monolayer may be repeated at q times until a desired thickness of the amorphous carbon polymer film is obtained before starting the plasma treatment process, wherein q is an integer of 1 to 50 (preferably 3 to 35), depending on the intended use of the film, etc., so as to deposit the amorphous carbon polymer film having a thickness of 1 nm to 15 nm (preferably 5 nm to 10 nm) before starting the plasma treatment process.

Next, the plasma treatment process begins, which comprises feeding a reforming gas (Ar and/or He) to the reaction space (“Stabilize”) which is excited by RF power (RF) to generate a plasma and reform the amorphous carbon polymer film without further depositing a polymer film (“RF Pulse-2”), followed by purging (“Purge”), wherein the reforming gas is fed continuously to the reaction space throughout the plasma treatment process. For example, RF power for the plasma reformation is in a range of 50 W to 1000 W (preferably 150 W to 500 W), which is equal to or higher than that used for the plasma polymerization, under a pressure of 100 Pa to 600 Pa (preferably 200 Pa to 400 Pa) which is lower than (e.g., less than half of) that used for the plasma polymerization. Typically, by the plasma treatment, the thickness of the film may be substantially unchanged or may be slightly decreased (e.g., more than 0%, less than 10%, more typically less than 5%).

In some embodiments, throughout the entire processes, the carrier gas is fed continuously to the reaction space in a range of 0 sccm to 2000 sccm (preferably 100 sccm to 500 sccm), for example. Also, the temperature of the processes may be in a range of −50° C. to 175° C. (preferably 35° C. to 150° C.).

The plasma-generating gas in the deposition process and the reforming gas in the plasma treatment process can be the same or different, e.g., both can be Ar and/or He.

Further, as necessary, the deposition process and the plasma treatment process are repeated at p times until the amorphous carbon polymer film having a desired thickness is obtained, wherein p is an integer of 1 to 120 (preferably 3 to 24), depending on the intended use of the film, etc., so as to deposit the final amorphous carbon polymer film having a thickness of 5 nm to 1000 nm (preferably 20 nm to 200 nm).

The continuous flow of the carrier gas can be accomplished using a flow-pass system (FPS) wherein a carrier gas line is provided with a detour line having a precursor reservoir (bottle), and the main line and the detour line are switched, wherein when only a carrier gas is intended to be fed to a reaction chamber, the detour line is closed, whereas when both the carrier gas and a precursor gas are intended to be fed to the reaction chamber, the main line is closed and the carrier gas flows through the detour line and flows out from the bottle together with the precursor gas. In this way, the carrier gas can continuously flow into the reaction chamber, and can carry the precursor gas in pulses by switching between the main line and the detour line. FIG. 1B illustrates a precursor supply system using a flow-pass system (FPS) according to an embodiment of the present invention (black valves indicate that the valves are closed). As shown in (a) in FIG. 1B, when feeding a precursor to a reaction chamber (not shown), first, a carrier gas such as Ar (or He) flows through a gas line with valves b and c, and then enters a bottle (reservoir) 20. The carrier gas flows out from the bottle 20 while carrying a precursor gas in an amount corresponding to a vapor pressure inside the bottle 20, and flows through a gas line with valves f and e, and is then fed to the reaction chamber together with the precursor. In the above, valves a and d are closed. When feeding only the carrier gas (noble gas) to the reaction chamber, as shown in (b) in FIG. 1B, the carrier gas flows through the gas line with the valve a while bypassing the bottle 20. In the above, valves b, c, d, e, and f are closed.

The process cycle can be performed using any suitable apparatus including an apparatus illustrated in FIG. 1A, for example. FIG. 1A is a schematic view of a PEALD apparatus, desirably in conjunction with controls programmed to conduct the sequences described below, usable in some embodiments of the present invention. In this figure, by providing a pair of electrically conductive flat-plate electrodes 4, 2 in parallel and facing each other in the interior 11 (reaction zone) of a reaction chamber 3, applying HRF power (13.56 MHz or 27 MHz) 25 to one side, and electrically grounding the other side 12, a plasma is excited between the electrodes. A temperature regulator is provided in a lower stage 2 (the lower electrode), and a temperature of a substrate 1 placed thereon is kept constant at a given temperature. The upper electrode 4 serves as a shower plate as well, and reactant gas and/or dilution gas, if any, and precursor gas are introduced into the reaction chamber 3 through a gas line 21 and a gas line 22, respectively, and through the shower plate 4. Additionally, in the reaction chamber 3, a circular duct 13 with an exhaust line 7 is provided, through which gas in the interior 11 of the reaction chamber 3 is exhausted. Additionally, a transfer chamber 5 disposed below the reaction chamber 3 is provided with a seal gas line 24 to introduce seal gas into the interior 11 of the reaction chamber 3 via the interior 16 (transfer zone) of the transfer chamber 5 wherein a separation plate 14 for separating the reaction zone and the transfer zone is provided (a gate valve through which a wafer is transferred into or from the transfer chamber 5 is omitted from this figure). The transfer chamber is also provided with an exhaust line 6. In some embodiments, the deposition of multi-element film and surface treatment are performed in the same reaction space, so that all the steps can continuously be conducted without exposing the substrate to air or other oxygen-containing atmosphere.

In some embodiments, in the apparatus depicted in FIG. 1A, the system of switching flow of an inactive gas and flow of a precursor gas illustrated in FIG. 1B (described earlier) can be used to introduce the precursor gas in pulses without substantially fluctuating pressure of the reaction chamber.

In some embodiments, a dual chamber reactor (two sections or compartments for processing wafers disposed close to each other) can be used, wherein a reactant gas and a noble gas can be supplied through a shared line whereas a precursor gas is supplied through unshared lines.

The film having filling capability can be applied to various semiconductor devices including, but not limited to, cell isolation in 3D cross point memory devices, self-aligned Via, dummy gate (replacement of current poly Si), reverse tone patterning, PC RAM isolation, cut hard mask, and DRAM storage node contact (SNC) isolation.

EXAMPLES

In the following examples where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. A skilled artisan will appreciate that the apparatus used in the examples included one or more controller(s) (not shown) programmed or otherwise configured to cause the deposition and reactor cleaning processes described elsewhere herein to be conducted. The controller(s) were communicated with the various power sources, heating systems, pumps, robotics, and gas flow controllers or valves of the reactor, as will be appreciated by the skilled artisan.

Example 1

An amorphous carbon polymer film was deposited on a Si substrate (having a diameter of 300 mm and a thickness of 0.7 mm) by PEALD-like process which is defined in U.S. patent application Ser. No. 16/026,711, each deposition cycle of which was conducted as the deposition process illustrated in FIG. 5 under the conditions shown in Table 1 below using the apparatus illustrated in FIG. 1A and a gas supply system (FPS) illustrated in FIG. 1B. As the reformation process as illustrated in FIG. 5 was conducted after every 12 cycles of the PEALD-like process (q=12), under the conditions shown in Table 2 below, which was conducted in the same reaction chamber as in the deposition process. The above combined cycles were repeated 24 times (p=24). The total (final) thickness of the film was roughly 100 nm.

TABLE 1 Temp. setting SUS temp (° C.). 68 SHD temp (° C.) 75 Wall temp (° C.) 75 BLT temp (° C.) RT Depo Pressure (Pa) 1100 Gap (mm) 14 Feed time (s) 0.4 Purge (s) 0.1 RF time (s) 1.5 Purge (s) 0.1 RF power (W) 175 Precursor cyclopentene Carrier He Carrier flow (slm) 0.1 Dry He (slm) 0.2 Seal He (slm) 0.1 (numbers are approximate)

TABLE 2 No reformation Reformation with Reformation with (“STD”) Ar (“Ar”) He (“He”) Cycle frequency — Every 5 nm Every 5 nm Reforming gas — Ar only He only Pressure — 300 Pa 350 Pa RF power — 300 W 175 W Duration of RF — 30 sec. 30 sec. (numbers are approximate)

In the reformation process, the amorphous carbon polymer film was exposed to an Ar plasma (“Ar”) or a He plasma (“He”) every time once the film thickness increased by about 5-nm increments (a ratio of deposition cycle to reformation cycle was 12). As a comparative example, no reformation process was conducted in “STD”, i.e., the amorphous carbon polymer film was deposited without the reformation process. Each of the resultant amorphous carbon polymer films (three “STD” films, one “Ar” film, and two “He” films) was annealed under one of the conditions shown in Table 3 below, in order to evaluate thermal stability of each film (film shrinkage after anneal).

TABLE 3 Anneal 1 Anneal 2 Anneal 3 (N2 200 C./ (N2 300 C./ (Vac 300 C./ 30 min) 60 min) 80 min) Atmosphere N₂ N₂ No gas flow Pressure 400 Pa 400 Pa 3 Pa Temperature 200° C. 300° C. 300° C. Duration 30 min. 60 min. 80 min. (numbers are approximate)

The results are shown in FIG. 2. FIG. 2 is a graph showing shrinkage of the amorphous carbon films without plasma treatment (“STD”), with the Ar plasma treatment (“Ar”), and with the He plasma treatment (“He”) after annealing. As shown in FIG. 2, the amorphous carbon polymer films formed using the Ar or He plasma cyclic treatment showed surprisingly low shrinkage in the various annealing conditions, indicating high thermal stability, as compared with the amorphous carbon polymer films formed without plasma cyclic treatment.

FIG. 3 shows Fourier Transform Infrared (FTIR) spectrums of the amorphous carbon films without plasma treatment (“STD”), with the Ar plasma treatment (“Ar”), and with the He plasma treatment (“He”) (before being subjected to the annealing). As shown in FIG. 3, the amorphous carbon polymer films formed using the Ar or He plasma cyclic treatment showed a significant decrease of H-related peaks, wherein the Ar or He plasma cyclic treatment reduced thermally unstable methyl and methylene fractions, as compared with the amorphous carbon polymer films formed without plasma cyclic treatment.

Example 2

Amorphous carbon polymer films (“STD”, “Ar”, and “He”) were formed in the same manner as in Example 1, and properties of the resultant amorphous carbon polymer films were evaluated. The results are shown in Table 4 below.

TABLE 4 STD-film Ar-film He-film RI  1.54 1.53 1.63 Water Contact Angle [°] (25° C.) 66.1 78.9 60.6 Stress [MPa] ^(~)0   −120 −440 RBS [%] C 51.0 51.0 54.0 H 46.0 47.0 39.0 O  3.0 2.0 7.0 N ND ND ND Thermal  50° C./30 min 0  — — shrinkage [%] 125° C./30 min 10-20 — — 200° C./30 min 17.6 7.1 0.6 300° C./30 min 35.4 5.4 0 (numbers are approximate)

As shown in Table 4, the thermal shrinkage of the amorphous carbon polymer film with the He plasma treatment (“He-film”) was remarkably lower than that of the amorphous carbon polymer film without plasma treatment (“STD-film”), wherein the thermal shrinkage of the He-film was substantially zero, indicating that the thermal stability of the He-film was excellent. In addition to the results shown in the FTIR of FIG. 3, considering the data in Table 4 showing that the He plasma treatment affected the properties of the film in a manner that RI of the He-film was higher than that of the STD-film, the water contact angle of the He-film was lower than that of the STD-film, the stress of the He-film was highly compressive as compared with that of the STD-film, and the C content of the He-film was higher than that of the STD-film whereas the H content of the H-film was lower than that of the STD-film, the He plasma treatment was likely to have promoted further polymerization of the film matrix, thereby reducing thermally unstable hydrogen-related fractions such as methyl and/or methylene fractions from the amorphous carbon polymer film, and reducing hydrogen bonds at the surface. It should be noted that oxygen atoms were detected in each film, and it may be because the films were exposed to air after the substrates were taken out from the reaction chamber.

Interestingly, according to the data in the FTIR of FIG. 3 and data shown in Table 4 as analyzed in a manner similar to that in the He plasma treatment, in the Ar plasma treatment, polymerization appears to be less progressed than in the He plasma treatment, wherein polymerization progressed to a certain degree, reducing hydrogen bonds in the film matrix, whereas hydrogen bonds on the surface increased (more hydrogenation on the surface). Thus, although the composition of the Ar-film appears to be substantially the same as that of the STD-film, the chemical structures of the films associated with hydrogen are considered to be different, wherein the Ar-film is more thermally stable than the STD-film but is less thermally stable than the He-film. In some embodiments, Ar-films and He-films are a hydrogenated amorphous carbon polymer having a composition constituted by more than 50% of carbon atoms and more than 35% but less than 50% of hydrogen atoms (as measured using, e.g., Rutherford backscattering Spectrometry (RBS)), wherein thermal shrinkage is less than 10% (preferably less than 5%) as measured when being placed in an atmosphere of N₂ under a pressure of 400 Pa at a temperature of 300° C. for 30 minutes as reference/standard conditions.

Example 3

An amorphous carbon polymer film was deposited on a Si substrate (having a diameter of 300 mm and a thickness of 0.7 mm) with a SiO liner having narrow/deep trenches with an opening of approximately 50 nm, which had a depth of approximately 90 nm (an aspect ratio was approximately 1.8), and narrow/shallow trenches with an opening of approximately 5 to 10 nm, which had a depth of approximately 90 nm, in the same manner as in the reformation with He in Example 1 except that the He plasma treatment was conducted after approximately every 10 nm (24 cycles of deposition) as measured on a planar surface (as blanket deposition).

FIG. 4 shows a STEM photograph of a cross-sectional view of the trenches subjected to the gap-fill process (bottom-up deposition) with the He plasma treatment, wherein arrows show slightly darker interfaces indicative of the He plasma treatment. Although the darker interfaces are indicative of the He plasma treatment, they do not represent layers reformed by the He plasma treatment, i.e., the reformation effect penetrates beyond the interfaces and reaches deeper portions of layers between the adjacent interfaces. In this example, the SiO liner was used in order to reduce the CD of the structure, and the SiO liner was the only layer which was conformal. As indicated by the arrows, although the He plasma treatment was cyclically conducted after every approximately 10 nm as measured on a planar surface, in the trenches, the viscous liquid-like behavior of amorphous carbon polymer is observed wherein the distance between the adjacent interfaces is significantly larger in the trenches than above the trenches. Interestingly, the distance between the adjacent interfaces gradually increases from the bottom as the film growth progresses and becomes the largest in the middle of the trenches in depth, and then gradually decreases toward the top of the trenches, indicating that the amorphous carbon polymer behaved as viscous liquid. Further, the film filled faster in the narrow trenches than in the wider trenches, indicating volumetric growth. Since the He plasma treatment formed darker interfaces which function as deposition markers, the above behavior can readily be observed in the STEM photograph. Typically, the plasma reformation effect reaches to a depth of about 10 nm, for example, and thus, inside the trenches where the distance between the adjacent interfaces is more than 10 nm, the plasma reformation effect can be considered insufficient; however, it appears that portions of film, which are temporarily deposited on the top and the sidewall of trenches and exposed to an Ar/He plasma, move downward to fill the trenches, and thus, it is expected that each amorphous carbon polymer layer may be relatively homogenous even if their thickness is over 10 nm inside the trenches (interfaces adjacent to the sidewalls and the top of the trenches are not as clear as those away from the sidewall and the top).

It will be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention. 

We/I claim:
 1. A method for reforming an amorphous carbon film as part of a deposition process thereof, comprising process of: (i) depositing an amorphous carbon film on a substrate in a reaction space until a thickness of the amorphous carbon film reaches a predetermined thickness, and then stopping the deposition process; and (ii) exposing the amorphous carbon film to an Ar and/or He plasma in an atmosphere substantially devoid of hydrogen, oxygen, and nitrogen.
 2. The method according to claim 1, wherein processes (i) and (ii) are repeated multiple times until a thickness of the amorphous silicon film reaches a desired final thickness.
 3. The method according to claim 1, wherein the predetermined thickness in process (i) is a monolayer thickness or more but 10 nm or less.
 4. The method according to claim 1, wherein the atmosphere in process (ii) is in the reaction space used in process (i).
 5. The method according to claim 1, wherein the atmosphere in process (ii) is in another reaction space different from the reaction space used in process (i).
 6. The method according to claim 1, wherein process (ii) comprises: feeding Ar and/or He to the atmosphere without feeding hydrogen, oxygen, and nitrogen; and applying RF power to the atmosphere in a manner generating the Ar and/or He plasma.
 7. The method according to claim 6, wherein RF power is in a range of 0.06 W/cm² to 0.96 W/cm² per unit area of the substrate, and a duration of process (ii) is in a range of 2 seconds to 300 seconds.
 8. The method according to claim 1, wherein process (i) is conducted by plasma-enhanced atomic layer deposition (PEALD).
 9. The method according to claim 1, wherein the substrate has a patterned recess or step on its surface on which the amorphous carbon film is deposited. 